Lift Arm of Skid Steer Loader

ABSTRACT

The lift arm of a skid steer loader according to the present invention has a simple structure. A pair of left and right lift arms each has a first arm portion and a second arm portion. The first arm portion is made as an elongated member from components made from plate metal or the like, and its base end is rotatably fitted to a support portion which projects upwards at a rear portion of the main body of the loader. In this second arm portion, a connection portion, an attachment fitting portion, a horizontal load bearing portion, and an actuator fitting portion and so on are integrally formed as one member from cast metal. Furthermore, a hollow portion is formed in the interior of this second arm portion, extending from an approximately intermediate portion thereof to its base end.

TECHNICAL FIELD

The present invention relates to a lift arm of a skid steer loader.

BACKGROUND ART

Since, with a skid steer loader, the direction is controlled according to difference between the rotation of the left and the right wheels, which is the feature by which such a skid steer loader differs from a wheel loader, and since moreover the lift arms are supported by the rear portion of the loader main body, accordingly it is possible to make the total length shorter (Patent Document #1). Because of this, it is possible to make a skid steer loader more compact than a wheel loader, and it is possible to make the radius of its turning circle smaller. Due to this, a skid steer loader is appropriately employed for civil engineering work in a comparatively restricted space such as, for example, landscaping or the like.

It should be understood that, while the lift arm of a conventional skid steer loader is built up from a group of components which are formed of rolled steel, among construction machines other than skid steer loaders, some working machines are also known in which a portion thereof is manufactured from cast metal (Patent Documents #2 and #3).

Patent Document #1: Japanese Laid-Open Patent Publication Heisei 6-33476.

Patent Document #2: Japanese Laid-Open Patent Publication Heisei 8-113960.

Patent Document #3: Japanese Laid-Open Patent Publication 2001-303606.

SUMMARY OF THE INVENTION Problem at the Solution of which the Invention is Directed

According to the above, with a skid steer loader, the radius of the turning circle is smaller as compared to a wheel loader, and it is also possible to perform a spin turn. Thus a skid steer loader, which is more compact and moreover whose ease of use is higher as compared to a wheel loader, can be utilized for various applications, such as ground leveling work or the like, in comparatively restricted spaces.

In some cases, such as, for example, when work such as digging or cutting work or loading work is being performed with a bucket which is provided at the end of a lift arm, and in some other cases, ground leveling work or the like may be performed by employing the side of the bucket or the like. In other words since, with a skid steer loader, the same working attachment may be used for various different applications, in which respect a skid steer loader is different from a wheel loader, accordingly, in addition to the load at the end of the lift arm in the vertical direction, a comparatively large load may also be experienced from the horizontal direction. Due to this, various structures must be provided at the end of the lift arm of a skid steer loader, i.e. a structure for sustaining loads from the vertical direction and a structure for sustaining loads from the horizontal direction, and accordingly the construction becomes complicated.

It should be understood that although, in Patent Documents #2 and #3 described above, it is disclosed to make a portion of a working machine out of cast metal, since these documents relate to a wheel loader and to an oil pressure shovel, accordingly they are not considered to have any specific connection with the particular technical nature of a skid steer loader such as described above.

The present invention has been conceived of in consideration of the problem described above, and its objective is to provide a lift arm of a skid steer loader, with which the construction of the lift arm can be simplified. Another objective of the present invention is to provide a lift arm of a skid steer loader, which is adapted so that it is possible to simplify and to lighten the construction at the end of the lift arm.

Means for Solving the Problems

The lift arm of a skid steer loader according to the present invention includes a first arm portion, a base end of which is rotatably supported at a rear portion of a loader main body, and the other end of which is formed so as to extend towards the front of the loader main body, and a second arm portion, a base end of which is fixed to the other end of the first arm portion, and the other end of which is formed so as to extend downwards. And, in the second arm portion, a connection portion which is fitted to the other end of the first arm portion, an attachment fitting portion which is provided at the other end, and to which a working attachment is rotatably fitted, an actuator fitting portion which is provided at the base end, and to which an actuator for actuating the working attachment is fitted, and a horizontal load bearing portion which is positioned between the attachment fitting portion and the actuator fitting portion, which is provided so as to project towards the side of the loader main body, and which is connected via a front member to a second arm portion on the opposite side of the loader main body, are made as a single unit in an integrated manner from cast metal. Furthermore, at the second arm portion, it is also possible to provide a hollow portion which extends from the connection portion to the horizontal load bearing portion.

Benefits of the Invention

According to the present invention, it is possible to simplify the construction of the lift arm, since the lift arm is separated into the first arm portion and the second arm portion, and the second arm portion, which is positioned towards the end thereof, is formed in one piece from cast metal.

Moreover, by providing the hollow portion to the second arm portion, it is possible to lighten the second arm portion.

Preferred Embodiment for Implementation of the Invention

In the following, an embodiment of the present invention will be explained based upon the drawings. In this embodiment, as described in detail hereinafter, the end portions of the lift arms, in other words the portions thereof forward from the regions where the actuator cylinders are fitted thereto, are formed from cast metal as one piece members. First of all, this skid steer loader as a whole will be explained, and then the construction of its lift arms will be explained.

FIG. 1 is a side view of a skid steer loader 1. And FIG. 2 is a plan view of this skid steer loader 1. As will be described hereinafter, this skid steer loader 1 comprises, for example, a loader main body 2, front wheels 3A and rear wheels 3B, a driver's seat 4, a support portion 5, lift arms 6, arm cylinders 7, an attachment coupler 8, a bucket 9, and the like.

The loader main body 2 constitutes the vehicle body of this skid steer loader 1, and front wheels 3A, 3A are provided to its front on the left and right sides so as to be rotatable, while rear wheels 3B, 3B are provided to its rear on the left and right sides so as likewise to be rotatable. The rotational speeds of the left and right front wheels 3A and rear wheels 3B can each be controlled independently. By varying the rotational speeds of the left and right front wheels 3A and rear wheels 3B, it is possible to control the attitude of the loader main body 2, and it is also possible to perform a spin turn. This type of rotational speed control of the vehicle wheels 3A and 3B can be performed with an actuation lever device at the driver's seat 4.

The driver's seat 4 is provided at an upper portion of the loader main body 2, positioned towards the front thereof. Except for its front surface, the other three surfaces of this driver's seat 4 (its left and right surfaces and its rear surface) are covered with net guards 4A. The operator gets into the driver's seat 4, and gets out therefrom, by using its front surface, which opens. Furthermore, at least a portion at the upper surface of the driver's seat 4 is covered with a ceiling portion 4B which is formed as a grid. It should be understood that it is not necessary to cover over all of the three surfaces of the driver's seat 4 apart from its front surface with the net guards 4A; any structure may be utilized, provided that the field of vision can be ensured, and moreover that the operator is able to mount and dismount.

An engine and the like is housed in the rear portion of the loader main body 2; and furthermore, at left and right rear portions of the loader main body 2 on both its sides, support portions 5, 5 for supporting the base ends of lift arms 6,6 are each provided so as to extend upwards. The base ends of lift arms 6 are supported by pins 12 at the upper ends of these support portions 5, so as to be rotatable.

The lift arms 6 are rotated in the upwards and downwards direction by the extension and retraction operation of arm cylinders 7. The base ends of these arm cylinders 7 are rotatably supported via pins 11 at the lower sides of the support portions 5, and the other ends of the arm cylinders 7 are rotatably supported via pins 13 at approximately the central portions of the lift arms 6. By the arm cylinders 7 extending, the lift arms 6 are displaced in the upward direction, as shown by the double dotted broken lines in FIG. 1. And, by the arm cylinders 7 retracting, the lift arms 6 are displaced downwards, as shown by the solid lines in FIG. 1.

The ends of the lift arms 6 are curved downwards towards the front of the loader main body 2, and an attachment coupler 8 is provided thereto. This attachment coupler 8 is a device for fitting various types of removable attachment, such as a bucket, a fork, a sweeper, or the like.

A bucket 9 which is fitted to the ends of the lift arms 6 via the attachment coupler 8 is an example of a working attachment, but the present invention is not limited thereto. When the lift arms 6 are lowered to their lowermost positions, for example, the angle θ1 between the front surface of the bucket 9 and the surface of the ground may be about 30°. Furthermore, as shown by the dotted lines in FIG. 1, when a load in the bucket 9 is to be loaded upon a truck or the like, the angle θ2 between the front surface of the bucket 9 and the surface of the ground may be, for example, about 45°.

In other words, as compared with a typical wheel loader, the angle to which the bucket 9 can rotate is set to be greater. Although a skid steer loader 1 is made to be more compact than a wheel loader, since the height of the carrier such as a truck upon which material is to be loaded does not change, accordingly the angle to which the bucket 9 can rotate is set to be greater, so that it is possible to perform loading work smoothly.

Here, it is desirable for the distance L1 between the center of gravity of the bucket 9 and the centers of the front wheels 3A to be set to be as short as possible. If L1 is set to be long, i.e. if the amount by which the lift arms 6 project forwards of the loader main body 2 is long, then, in order to obtain a balance, it is necessary to mount a balance weight to the rear portion of the loader main body 2. If such a balance weight is mounted, then the weight of the skid steer loader 1 increases, its overall dimensions are increased, and its working ability is decreased. Accordingly, it is desirable for L1 to be set to be as short as possible.

However, the shorter L1 is set, the less easy does it become to ensure sufficient space for reinforcing the left and right lift arms 6, 6 with Z-shaped link members or the like. Since the left and right lift arms 6, 6 are curved somewhat downwards towards the loader main body 2, accordingly the gap between the ends of these lift arms 6, 6 and the front end of the loader main body 2 becomes short, and the space for reinforcing them with link members or the like becomes tight. Furthermore, since the operator gets into and gets out of this skid steer loader 1 through the front of the loader main body 2, which is different from the case with a wheel loader, accordingly it is also necessary to employ a construction in which no impediment is presented to the operator getting in and out.

Thus, in this embodiment, as will be described subsequently, with this skid steer loader 1 in which there is a scarcity of space between the lift arms 6, 6 for reinforcement, a new construction for the lift arms 6 is proposed, with which it is possible sufficiently to withstand horizontal load applied to the lift arms 6, and with which, moreover, it is possible to anticipate lightening thereof.

FIG. 3 is a perspective view of the lift arms 6, and FIG. 4 is a plan view of these lift arms 6. As shown in the perspective view of FIG. 3, one of these lift arms 6 is made from a first arm portion 21 and a second arm portion 22. The first arm portion 21 is formed from a material such as steel plate or the like as an elongated member having a generally rectangular shape in cross section, while the second arm portion 22 is formed in a curved shape from cast metal such as, for example, SC450W or the like. First the structure of the first arm portion 21 will be explained, and next the structure of the second arm portion 22 will be explained.

A base end 21A of the first arm portion 21 is fitted via one of the pins 12 to the upper side of one of the support portions 5 so as to be freely rotatable, while its other end 21B is fixed to a base end 22A of the second arm portion 22 using a fixing means such as welding or the like. At an approximately intermediate portion of the first arm portion 21, a cylinder fitting portion 21C is provided so as to extend downwards. And the end of one of the arm cylinders 7 is rotatably supported upon this cylinder fitting portion 21C via one of the pins 13.

The second arm portion 22, while being fitted to the end 21B of the first arm portion 21, is curved downwards so as to cover the upper side of one front wheel 3A of the loader main body 2. By contrast to the first arm portion 21 which is made by welding together a plurality of metallic plates, this second arm portion 22 is made as one unitary piece of cast metal.

In this second arm portion 22, there are integrally formed from cast metal a connection portion 22A, an attachment fitting portion 22B, a horizontal load bearing portion 22C, and an actuator fitting portion 22D, each of which will be described hereinafter.

The connection portion 22A is provided as positioned at the base end of the second arm portion 22, and it is fitted to the end 21B of the first arm portion 21. And the attachment fitting portion 22B is provided as positioned at the other end of the second arm portion 22, with the bucket 9 being fitted to it via the attachment coupler 8.

The horizontal load bearing portion 22C is positioned at an approximately intermediate portion of the second arm portion 22, and is provided so as slightly to project to the inside (i.e. to the side of the loader main body 2). One end of a front member 30, which is made by, for example, metallic plate processing or the like, is connected to the projecting end side of this horizontal load bearing portion 22C. In other words, the left and right second arm portions 22, 22 are connected together via the front member 30 which is connected to their horizontal load bearing portions 22C. Accordingly, the front member 30 may also, for example, be termed an arm connection portion. Furthermore, a reinforcement portion 22C1 is provided upon the upper surface of the horizontal load bearing portion 22C, extending slantingly upwards towards the inner side of the second arm portion 22. Load which is imposed upon the second arm portion 22 from the horizontal direction (the transverse direction to the loader main body 2) is transmitted from the horizontal load bearing portion 22C via the front member 30 to the second arm portion 22 on the other side. The reinforcement portion 22C resolves the load which the second arm portion 22 receives from the horizontal direction into component forces in the vertical direction and in the horizontal direction, and prevents the stress being concentrated in any particular spot.

The actuator fitting portion 22D is provided as positioned towards the base end of the second arm portion 22, and so as to project somewhat upwards. This actuator fitting portion 22D is a lug for rotatably attaching the base end of an actuator cylinder not shown in the figure.

Furthermore, ribs 22E may be provided upon the surface of the second arm portion 22 as appropriate. In the example shown in the figures, the rigidity of the end 22B of the second arm portion 22 is enhanced by providing a plurality of ribs 22E as positioned towards the end 22B.

FIG. 5 is a side view of a lift arm 6 as seen from the exterior of the loader main body 2, and FIG. 6 is a side view of the end portion of a lift arm 6 as seen from the interior of the loader main body 2. As already explained, this lift arm 6 is built in a hybrid construction, and includes an elongated first arm portion 21 which is made by processing metal plate or the like, and a second arm portion 22 which is made from cast metal. And the second arm portion 22 is made as a single unitary component, in which a connection portion 22A, an attachment fitting portion 22B, a horizontal load bearing portion 22C, and an actuator fitting portion 22D and so on are formed in an integrated manner.

Furthermore, as shown in the sectional view of FIG. 7, in this embodiment, a hollow portion 22F is provided in the interior of the second arm portion 22. This hollow portion 22F is formed so as to extend from the base end of the second arm portion 22 (i.e. the connection portion 22A) to a point P which is roughly intermediate along the second arm portion 22. This point P may be, for example, set so as to match the lower edge of the horizontal load bearing portion 22C.

Naturally, it is not absolutely required for the hollow portion 22F to be provided as far as the lower edge of the horizontal load bearing portion 22C; it would be acceptable for the length L2 of this hollow portion 22F to be shorter. However, the shorter the length L2 of the hollow portion 22F (its length in the longitudinal direction from the connection portion 22A towards the attachment fitting portion 22B) is made, the more is the weight of the second arm portion 22 increased.

The horizontal cross sectional size of this hollow portion 22F is set from the point of view of ensuring the rigidity of the portion which includes this hollow portion 22F. In other words, the thickness t of the second arm portion over the range where the hollow portion 22F is provided is set to a value at which the necessary rigidity thereof is assured.

In this embodiment, as described above, the lift arm 6 is made in a construction which is divided into two portions, the first arm portion 21 and the second arm portion 22; and, moreover, the second arm portion 22 is made as a unitary member from cast metal. Accordingly, it is possible to simplify the structure of the second arm portion 22, whose construction can easily become complicated, and, as a result, it is possible to simplify the overall structure of the lift arm 6. Due to this, it is possible to reduce the number of component parts of the lift arm 6, so that it is possible to enhance the production efficiency and to reduce the manufacturing cost.

In other words, this skid steering loader 1 is a device which can be handily used in various applications in a comparatively restricted space, in which characteristic it differs from a wheel loader, and it has the technical nature that not only is a load imposed upon it in the vertical direction, but also comparatively high loads may be applied to it in the horizontal direction as well.

Moreover, with a skid steer loader 1, in order to enhance the working characteristics in a comparatively restricted space, there is a demand from the market to make it more compact and lighter. Accordingly, as shown in FIG. 1, the distance L1 between the center of gravity of the bucket 9 and the centers of the front wheels 3A is set to be short, and therefore the availability of space for providing reinforcement structures like Z-shaped link members or the like becomes poor.

Under this type of limitation, with a skid steer loader 1, it is necessary to provide lift arms 6, 6 which have a structure and so on which takes effective advantage of the small space available, in order to provide a structure for fitting an actuator such as the bucket 9 or the like, and in order adequately to support loads both in the vertical direction and also in the horizontal direction. With prior art skid steer loaders, since various groups of components made from plate metal have been disposed in this limited space, the construction of the lift arms has become complicated, and the efficiency of the assembly process for them has also been low. By contrast, with this embodiment of the present invention, since the second arm portion 22 which is made as a single unitary member from cast metal is disposed in this limited space, it is possible to simplify the construction and to enhance the production efficiency, and it is also possible to reduce the manufacturing cost.

Moreover, in this embodiment, it is arranged to provide the hollow portion 22F within the second arm portion 22 while still ensuring adequate rigidity for the second arm portion 22. Due to this, it is possible to anticipate that the second arm portion 22 will be lightened.

It should be understood that the present invention is not limited to the embodiment described above. It would be possible for a person skilled in the art to make various additions or changes or the like, within the range of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a skid steer loader;

FIG. 2 is a plan view of this skid steer loader;

FIG. 3 is a perspective view of lift arms thereof;

FIG. 4 is a plan view of these lift arms;

FIG. 5 is a side view of a lift arm as seen from the exterior;

FIG. 6 is a side view of the end portion of a lift arm as seen from the interior; and

FIG. 7 is a sectional view of a second arm portion.

EXPLANATION OF THE REFERENCE SYMBOLS

1 . . . skid steer loader, 2 . . . loader main body, 3A . . . front wheels, 3B . . . rear wheels, 4 . . . driver's seat, 4A . . . net guards, 4B . . . ceiling portion, 5 . . . support portions, 6 . . . lift arms, 7 . . . arm cylinder, 8 . . . attachment coupler, 9 . . . bucket, 11, 12, 13 . . . pins, 21 . . . first arm portions, 21A . . . base ends, 21B . . . end portions, 21C . . . cylinder fitting portions, 22 . . . second arm portions, 22A . . . connection portions, 22B . . . attachment fitting portions, 22C . . . horizontal load bearing portions, 22C1 . . . reinforcement portions, 22D . . . actuator fitting portions, 22E . . . ribs, 22F . . . hollow portion, 30 . . . front member. 

1. A lift arm of a skid steer loader, comprising: a first arm portion, a base end of which is rotatably supported at a rear portion of a loader main body, and the other end of which is formed so as to extend towards a front of said loader main body; and a second arm portion, a base end of which is fixed to said other end of said first arm portion, and the other end of which is formed so as to extend downwards; wherein, in said second arm portion: a connection portion which is fitted to said other end of said first arm portion; an attachment fitting portion which is provided at said other end, and to which a working attachment is rotatably fitted; an actuator fitting portion which is provided at said base end, and to which an actuator for actuating said working attachment is fitted; and a horizontal load bearing portion which is positioned between said attachment fitting portion and said actuator fitting portion, which is provided so as to project towards a side of said loader main body, and which is connected via a front member to a second arm portion on the opposite side of said loader main body; are made as a single unit in an integrated manner from cast metal.
 2. The lift arm of a skid steering loader as described in claim 1, wherein, in said second arm portion a hollow portion is provided which extends from said connection portion to said horizontal load bearing portion. 